1. Field of the Invention
The present invention relates to valve devices that are preferably used for hydraulic control in hydraulic equipment such as automatic transmissions installed in vehicles.
2. Description of the Related Art
Today, valve devices equipped with solenoid actuators are used to open and close flow paths of hydraulic fluids for speed control in automatic transmissions installed in vehicles. One example of such valve devices is disclosed in Japanese Unexamined Patent Application Publication 2003-74729. This valve device includes a valve member and a solenoid. The valve member opens and closes an oil path, and the solenoid drives the valve member using a plunger. The oil path is opened or closed by driving the valve member, which is driven by turning on and off an electromagnetic force of the solenoid. Specifically, in such a valve device, when power is turned off, the plunger, which is urged by a spring, pushes the valve member against a sitting surface so as to close the oil path. When the power is turned on, an electromagnetic force of the solenoid causes the plunger to move back against the urging force of the spring. Thus, the valve member moves away from the sitting surface due to the oil pressure of a hydraulic fluid, thereby opening the oil path.